Stable fuel oil compositions



United States Patent STABLE FUEL 01L COMPOSHTIONS Henry A. Ambrose, Penn Township, Allegheny County, and OliverL. Bil-antics, Gibsonia, Pa., assignors .to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware N0 Drawing. Application March 28, 1950, Serial No. 152,517

'5 Claims. tci. 44-6s This invention relates to stable fuel oil compositions. More particularly, the invention relates to stable fuel oil compositions which are composed of straight run and catalytically cracked oils.

When a heavy petroleum oil is subjected to catalytic cracking by any of the conventional processes such as the fixed bed, moving bed or fluid processes, wherein the heavy oil is contacted with a cracking catalyst such as a natural clay catalyst or a synthetic silica-alumina or sllica-magnesia catalyst, the conversion products comprise not only gasoline hydrocarbons but also heavier distillate hydrocarbons, such as hydrocarbons boiling in the fuel oil range; that is, hydrocarbons boiling within the range of about 350 to about 750 F. Although the burning characteristics of such oils are fairly good, it is generally the practice when using these catalytically cracked oils as fuels to mix them with straight run distillate oils of similar boiling range in order to produce mixed oils having better burning characteristics than the catalytically cracked oils, and also in order to balance .refinery production.

These mixed straight run and catalytically cracked distillate oils, however, have been found to have the disadvantage of being relatively unstable in storage. After a few months in storage at atmospheric temperature, they tend to form a precipitate or sludge which is unsightly and which reduces their usefulness as burning oils in certain types of installations. It has been found that the storage characteristics of a mixed oil are poorer than the characteristics of either oil alone. The reason for this is not clearly understood, but it may be that the solubility of certain degradation products of the catalytically cracked oil is less in the mixed oil than in the catalytically cracked oil.

The present invention relates to fuel oil compositions comprising mixed catalytically cracked and straight run distillate fuel oils which compositions are of improved stability with respect to sludging characteristics and therefore of good appearance and adapted for effective use in fuel oil furnaces and :as diesel fuels even after being stored for extended periods. It has been discovered that such an improved mixed fuel oil composition can be obtained by' incorporating in the mixed oils a small amount of a combination of a zinc, calcium, barium or magnesium salt of a dialkyl dithiophosphoric acid in which the alkyl groups are open chain or cyclic alkyl groups containing 4 to 12 carbon atoms, and the calcium or barium salt of an oil soluble petroleum sulfonic acid. The zinc di-cycloalkyl dithiophosphates are especially valuable, a preferred member of the class being zinc dicyclohexyl dithiophosphate. and the calcium or barium sulfonate may be employed in varying proportions with respect to one another. It is generally preferred to add them in about equal proportions by weight, but other proportions can be used provided the compound present in the smaller amount present in an amount corresponding .to at least about 0.005 percent by weight of the mixed oils. In general, it is preferred to employ the compounds in weight ratios varying from 1:4 to 4:1.

It has not been determined in what way combinations of compounds of these classes function to improve the characteristics of the mixed fuel oil and therefore the invention is not limited to any theory of operation. It

might appear that they function as solubilizing agents for the sludge, but this function is more or less negatived by the fact that whereas amixed fuel oil in theabsence The zinc dithiophosphate of such a combination forms additional amounts of sludge so long as it is stored, at least over any feasible test storage period, the incorporation of a combination of this class in the oil inhibits the formation of sludge even after some sludge has been formed, and the already formed sludge does not disappear. By adding a small amount of a combination of compounds as described to a mixed fuel oil containing an amount of sludge making the oil undesirable for use in many burner installations because of sludge deposits, the oil can be employed in such installations without leaving undesirable deposits. In this case it appears that although the sludge does not disappear, its characteristics are so changed as to prevent its deposition on a typical burner screen or on other parts of a burner.

The addition of the combination in very small amounts has been found to produce the best results. Thus, fully effective results are obtained when using between about 0.025 and about 0.15 per cent of the combination by weight of the mixed fuel oil even when the mixed oils have high sulfur content and pronounced sludging tendencies. However, adequate results are obtained when using as little as 0.01 per cent of the combination. In this case, in many instances full inhibition of sludge formation is not obtained but the mixed oil is satisfactory for use because the combination changes the physical, and perhaps chemical, nature of the sludge so that it does not cause rapid clogging of screens and other parts of burners. While larger quantities than 0.15 per cent can be used, no advantage appears to result. The use of larger quantities necessarily increases the ash and carbon residue test values of the mixed oils, and sometimes also causes darkening.

The compounds may be incorporated in the mixed fuel oil in any suitable manner. For example, they may be added either separately or together to either or both of the catalytically cracked or straight run oils prior to mixing the two or they may be added to the mixed oil. When the compounds are incorporated in the mixed oil, it is unnecessary to do this immediately after mixing the oil as they are effective even after some sludge has formed. It will usually be preferable to add the compounds prior to any sludge formation as this will either eliminate sludge formation, or reduce the amount of sludge formed, depending upon the specific characteristics of the oils employed in making up the mixed oil. The compounds can be added as such but it is preferred to employ them in the form of a concentrated solution or concentrated solutions in an oil carrier. After addition, some circulation of the mixed oil is desirable to insure the early production of a uniform composition, but this is not absolutely necessary.

The problem with which the present invention is concerned exists only when a catalytically cracked oil and a straight run oil are combined in such proportions as to cause a substantial effect such as previously described. The invention is important when the ratio of the volume of the catalytically cracked oil to the straight run oil is within the range of 9:1 to 1:9. It is especially advantageous when applied to mixed oils containing these oils in a volume ratio within the range of 4:1 to 1:4.

In order to determine the effectiveness in mixed fuel oils of compounds of the classes disclosed above, two tests were carried out, a light stability test and a storage test. The light stability test was carried out by exposing a cc. sample of the oil to be tested to a light source rich in ultra-violet rays, for periods of 4 hours alternated with periods of 20 hours during which the oil was stored in the dark. The test was completed after- 40 hours exposure to the'light. At the end of each dark storage period the samples were examined for the pres ence of precipitated sediment or sludge. The exposure to light was accomplished by putting samples of fuel oil in 4-ounce' bottles which were unstopped to allow access of air. These bottles were placed within a citcular metal enclosure at a distance of 22 inches from the light source which was a Westinghouse 400 watt type DH1 mercury vapor lamp mounted vertically in the center of the housing. It was found that a temperature rise of 20 F. occurs during the exposure period. The interval of darkness was necessary to allow any dispersed sludge to settle and to permit oxygen to replace any used up in the light-induced reaction. The effect of the exposure to light was judged by swirling the bottle and estimating the quantity of precipitate which had settled. This was recorded as Trace, Light, Medium or Heavy.

The storage test was carried out by pouring 1500 cubic centimeters of the fuel to be tested into a two-quart Mason jar and immersing an 8 inch by 1 /2 inch by 4 inch SAE 1020 cold rolled steel strip in the oil. The steel surface to oil ratio approximates that existing in a 55 gallon steel drum. The jar was then closed with a vented lid and was stored in total darkness. Periodically sampling and testing were carried out as rapidly as possible in subdued light. The extent of deterioration of the fuel was determined by the amount of precipitate observed and designated as Trace, Light, Medium or Heavy. Any staining or corrosion of the steel strip was noted.

In the following table there are given the results of light stability and storage tests made on mixed fuel oils of the character indicated in the absence of an additive and containing compounds of the classes disclosed above. The compounds employed in these tests were the zinc salt of di-cyclohexyl dithiophosphoric acid, which is designated in the following table as Compound I, and the calcium salt of an oil-soluble petroleum sulfonic acid, which is referred to in the table as calcium sulfonate. These compounds were employed in the form of a 50 per cent solution in a hydrocarbon oil, but the percentages of each compound used in the tests are based on the weight of the compound itself.

The ratios of the oils employed are volume ratios and the percentages of the added compounds are percentages of the weight of the mixed oil. The term No. 2 indicates an oil boiling Within the range of about 350 to 750 F. and having a minimum API gravity of 26. The straight run oil employed had been caustic washed.

In the following table there are tabulated the results obtained in storage and light stability tests on the oils alone and stabilized fuel oil compositions of the invention.

From the results given in the foregoing table it will be seen that while the individual oils have reasonably good stability properties, the mixed oils possess poor stability properties. These results also show that mixtures of straight run and catalytically cracked oils are materially improved with respect to stability to sludge formation by the addition of combinations of Compound I and the calcium salt of oil-soluble petroleum sulfonic acids. The stability of the mixed oil to sludge formation is improved with the addition of as little as 0.0125 per cent of each compound; however, major improvement is obtained by the addition of 0.025 per cent. Substantially the same, and in some cases somewhat improved results are obtained when adding about 0.05 per cent of each compound. Also, stability to sludge formation is obtained when larger amounts are employed but no advantage is gained with the use of larger amounts and necessarily the ash and carbon residue test values of the finished oil are increased, which is undesirable. Therefore, when positive control of sludge formation is desired, it is preferred to employ at least 0.0125 per cent of each component and it is not necessary to employ more than 0.05 per cent. If the total amount of the combination is 0.10 per cent of the weight of the mixed oils and contains at least 0.0125 per cent of each component, effective control of sludge formation is obtained. In any case, because of undesirable color changes, the total amount of the two compounds should not exceed 0.25 per cent of the mixed oils.

The tests employed in obtaining the data set out in the table are especially severe tests of the compounded oils and the results are given in terms of the quantity of sludge deposited without regard to the nature of the sludge. In practice, however, the quantity of sludge formed is frequently not as important as the physical characteristics of the sludge. The addition of a very small amount of a combination of compounds of the classes described to a mixed fuel oil affects the characteristics of the sludge, making it lighter and apparently more easily dispersed so that sludge deposition is avoided or at least materially lessened. To accomplish variation in the nature of the Table Storage Test Light Stability Test Oil Precipitate Formed and Condition of Metal Strip Amount of Sludge at End of Test No. of Hours Exposure to Ultragipltet Light Required to Sludge 1 Month 3 Months fiMonths Trace Light Medium None, OK

Light, OK

Medium, OK

1. West Texas Straight Run No. 2 Fuel Oil.

2. Thermofor Catalvtically Cracked N0. 2 Distillate.

3. /50 Blend West Texas Straigh Run N0. 2 Fuel Oil and Thermofor Catalvtically Cracked No. 2 Distillate. No additive.

4. 50/50 Blend West Texas Straight Run No. 2 Fuel Oil and Thermoior Catalvt-ically Cracked No. 2 Distillate Plus 0.025% Composition I and 0.025% Calcium Sulfonate.

5. 50/50 Blend West Texas Straight Run No. 2 Fuel Oil and Thcrrnofnr Catalvtically Cracked No. 2 Distillate Plus 0.0125% of Composition I and 0.0125% Calcium Sulfonate.

6. /20 Blend West Texas Straight Run No. 2 Fuel Oil and Thermofor Catalytically Cracked No. 2 Distillate. No Additive.

7. 80/20 Blend West Texas Straight Run No. 2 Fuel Oil and Thermofor Catalytically Cracked No. 2 Distillate Plus 0.025% of Composition I and 0.025% Calcium Sulfonate.

8. 80/20 Blend We t Texas Straight Run No. 2 Fuel Oil and Thermofor Catalytically Cracked No. 2 Distillate Plus 0.0125% of Composition I and 0.0125% Calcium Sultanate.

Trace, 81. Stain.

Light, OK

Medium, Stained..-

Light, OK

Medium, OK

Light, StainecL Light, Sl. Stain Medium+ OK.

Trace, Stain Light, OK

Heavy, Stained.

Light, OK

Medium, OK.-.

Medium, Stained 4 Light, S1. Stain 4 8 Heavy, Rust 4 8 Trace+.

Medium.

Heavy.

Light, Rust 4 36 Light.

Heavy, OK 4 16 28 Medium.

Heavy, Stained 4 8 16 24 Heavy.

28 Light.

Light, Rust At Top.-. 4

12 32 Medium.

Medium, Rust Above 4 Oil Level.

sludge as well as some control over the actual formation of sludge, as little as 0.005 per cent by weight of the mixed oils of each component of the combination, or a total of 0.01 per cent of the combination, can be used. We generally prefer to employ each component in an amount equal to about 0.005 to about 0.05 per cent by weight of the mixed oils.

Although the compounds employed in the tests, the results of which are given in the table, are preferred for use in the fuel oil compositions of the invention, it will be understood that other members of the classes of compounds disclosed above may be used to prepare fuel oil compositions of substantially the same improved properties. Examples of other suitable dialkyl dithiophosphoric acid compounds are the zinc, barium, calcium and magnesium salts of di-2-ethylhexyl dithiophosphoric acid, di-n-hexyl dithiophosphoric acid, di-n-heptyl dithiophosphoric acid, didodecyl dithiophosphoric acid, di-isobutyl dithiophosphoric acid.

The oil-soluble petroleum sulfonic acids whose calcium or barium salts are employed in the oil compositions of the invention are preferably the sulfonic acids known as mahogany acids. These acids, together with the watersoluble green acids, are produced during the acid refining of lubricating oil distillates. Methods of recovering these acids, as well as methods of making the calcium or barium salts, are well known and form no part of the present invention.

If desired, the stable fuel oil compositions may contain in addition to the compounds previously discussed oxidation inhibitors, fiash point control agents, corrosion inhibitors, anti-foam agents, ignition quality improvers, combustion improvers and other additives adapted to improve the oils in one or more respects.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit or scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A fuel oil composition comprising a major proportion of a mixture of straight run and catalytically cracked distillate fuel oils tending to deposit sludge, wherein the straight run and catalytically cracked fuel oils are present in a volume ratio of between about 9:1 and about 1:9, and" containing a small amount of a combination of a member selected from the group consisting of the zinc, barium, calcium, and magnesium salts of a dialkyl dithiophosphoric acid in which the alkyl groups contain 4 to 12 carbon atoms and a member selected from the group consisting of the barium and calcium salts of oil-soluble petroleum sulfonic acids, said small amount being sufficient to inhibit sludge deposition from said mixture of oils and comprising at least 0005 per cent by weight of said mixture of oils of each of said salt of said dialkyl dithiophosphoric acid and said salt of said oil-soluble petroleum sulfonic acids and not more than 0.25 per cent of said combination by weight of said mixture of oils.

2. A fuel oil composition comprising a major proportion of straight run and catalytically cracked fuel oils tending to deposit sludge, wherein the straight run and catalytically cracked fuel oils are present in a volume ratio of between about 9:1 and about 1:9, and containing a small amount of a combination of zinc di-cyclohexyl dithiophosphate and a member selected from the group consisting of the barium and calcium salts of oil-soluble petroleum sulfonic acids, said small amount being sufficient to inhibit sludge deposition from said mixture of oils and comprising at least 0.005 per cent by weight of said mixture of oils of each of said zinc di-cyclohexyl dithiophosphate and said salt of said oil-soluble petroleum sulfonic acids, and not more than 0.25 per cent of said combination by weight of said mixture of oils.

3. A fuel oil composition comprising a major proportion of a mixture of straight run and catalytically cracked distillate fuel oils tending to deposit sludge, wherein the straight run and catalytically cracked fuel oils are present in a volume ratio of between about 9:1 and about 1:9, and containing a small amount of a combination of zinc di-cyclohexyl dithiophosphate and the calcium salt of oilsoluble petroleum sulfonic acids, said small amount being suflicient to inhibit sludge deposition from said mixture of oils and comprising at least 0.005 per cent by Weight of said mixture of oils of each of said zinc di-cyclohexyl dithiophosphate and said calcium salt and not more than 0.25 per cent of said combination by weight of said mixture of oils.

4. A fuel oil composition as defined in claim 3 in which each of said zinc di-cyclohexyl dithiophosphate and said calcium salt of oil-soluble petroleum sulfonic acids is present in an amount equal to about 0.005 to about 0.05 per cent by Weight of said mixture of oils.

A process for treating a composition consisting essentially of a mixture of straight run and catalytically cracked distillate fuel oils, wherein the straight run and catalytically cracked fuel oils are present in a volume ratio of between about 9:1 and about 1:9, from which sludge has begun to deposit, to prevent further substantial deposition of sludge which comprises introducing into said fuel oil composition a small amount of a combination of a member selected from the group consisting of the zinc, barium, calcium and magnesium salts of a dialkyl dithiophosphoric acid in which the alkyl groups contain from 4 to 12 carbon atoms and a member selected from the group consisting of the barium and calcium salts of oilsoluble petroleum sulfonic acids said small amount being sufficient to inhibit sludge deposition from said mixture of oils and comprising at least 0.005 per cent by weight of said mixture of oils of each of said salt of said dialkyl dithiophosphoric acid and said salt of said oil-soluble petroleum sulfonic acids and not more than 0.25 per cent of said combination by Weight of said mixture of oils.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,252,985 Rutherford et a1 Aug. 19, 1941 2,369,632 Cook et a1 Feb. 13, 1945 2,417,876 Lewis et al Mar. 25, 1947 2,524,864 Wies et al. Oct. 10, 1950 

1. A FUEL OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF A MIXTURE OF STRAIGHT RUN AND CATALYTICALLY CRACKED DISTILLATE FUEL OILS TENDING TO DEPOSIT SLUDGE, WHEREIN THE STRAIGHT RUN AND CATALYTICALLY CRACKED FUEL OILS ARE PRESENT IN A VOLUME RATIO OF BETWEEN ABOUT 9:1 AND ABOUT 1:9, AND CONTAINING A SMALL AMOUNT OF A COMBINATION OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF THE ZINC, BARIUM, CALCIUM, AND MAGNESIUM SALTS OF A DIALKYL DITHIOPHOSPHORIC ACID IN WHICH THE ALKYL GROUPS CONTAIN 4 TO 12 CARBON ATOMS AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF THE BARIUM AND CALCIUM SALTS OF OIL-SOLUBLE PETROELEUM SULFONIC ACIDS, SAID SMALL AMOUNT BEING SUFFICIENT TO INHIBIT SLUDGE DEPOSITION FROM SAID MIXTURE OF OILS AND COMPRISING AT LEAST 0.005 PER CENT BY WEIGHT OF SAID MIXTURE OF OILS OF EACH OF SAID SALT OF SAID DIALKYL DITHIOPHOSPHORIC ACID AND SAID SALT OF SAID OIL-SOLUBLE PETROLEUM SULFONIC ACIDS AND NOT MORE THAN 0.25 PER CENT OF SAID COMBINATION BY WEIGHT OF SAID MIXTURE OF OILS. 